This invention relates to address decoders in general, and specifically to address decoders for use with multichannel analyzers in conjunction with the recording of the natural gamma ray spectra of formations surrounding a well bore.
As is well known in the art, natural gamma rays produced by the earth formations provide an indication of the occurrence of the naturally occurring radioactive elements, such as thorium, potassium and uranium. Since these elements produce gamma rays having different energy levels, a well logging instrument having the capability for measuring the energy of such gamma rays, for example, one having a scintillation counter, thus provides a means of ascertaining the existence of such elements. It is also known in the art to record the total energy spectrum, such a recorded curve being generally referred to by those in the art as a natural gamma ray log.
In theory, at least, the only special surface instrumentation required for such logs are single channel analyzers. However, because it is desired to make very accurate recordings and since variations in logging cable characteristics with depth introduces signal amplitude changes, it has generally been considered necessary to use a multichannel pulse height analyzer in addition to the single channel analyzers to produce the log. The multichannel analyzer in such cases has generally served as a monitor, and the gain of the surface amplifier is adjusted, when necessary, to maintain a selected energy peak in a particular channel of the analyzer. For various other reasons, it has been found convenient and desirable to have a multichannel analyzer in the logging system. Furthermore, those in the art have generally been unable to utilize a multichannel analyzer to provide such logs without the use of one or more single channel analyzers.
It is therefore the primary object of the present invention to provide an address decoder for use with multichannel analyzers;
It is also an object of the invention to provide new and improved circuitry and apparatus for measuring and recording preselected portions of the energy spectrum of gamma rays emanating from earth formations surrounding a well bore;
It is also an object of the present invention to provide new and improved circuitry whereby a multichannel analyzer provides not only an energy spectrum of detected gamma rays but also provides means for measuring and recording a multiplicity of signals corresponding to preselected energy bands within the spectrum limits without the use of single channel analyzers; and
It is yet another object of the invention to provide new and improved circuitry for improving the efficiency of a multichannel analyzer.
The objects of the invention are accomplished, generally, with address decoder circuitry which compares the address scaler output of a multichannel analyzer with a predetermined reference and which provides pulse outputs based upon such comparison. As an additional feature, such address decoder circuitry provides means for intensifying the oscilloscope readout associated with the multichannel analyzer relating to the energy range of a given address decoder section.